On 4 Mar 2006 17:53:30 -0800, "Frank" wrote:

David wrote,
Do people find that the manufacture recommendations for their filters
(ex: for up to a 30 gallon tank) are accurate, or do they stretch that?

I think the best thing that has happened with filters over the past 40
years is the bio-wheels - they remove DOCs where other hang-on power
filters without the bio-wheels don't. I would however, well over-size
the filter on any fish tank, and on tank of 55 gal. and up, use two
over sized filters................... Frank

Comparing the gph - gallons per hour - of various filters, instead of
tank size ratings, might give you a better handle on capabilities of
different brands. I compared a few of the popular brands and found
that their rated tank sizes did not always agree in gph. Different
brands might determine that 3 complete turnovers of a tank's water is
sufficient, while another company might rate their filters using 5
turnovers of water per hour. So the hypothetical 30 gallon tank might
be matched with 90 or 100 gph by one brand, but 150 gph by another
brand. Aquaclear and Whisper were pretty consistent, basing their tank
ratings on 5 tank turnovers an hour. Others varied, sometimes within a
brand; a rating of 5 turnovers an hour might be used for smaller tanks
while only three turnovers an hour was good for, in their opinion,
larger tanks. So recommended tank size for a given filter is
subjective and will be forever debated, gallons per hour is a
measurable, objective rating.

-- Mister Gardener